The production of vocal sounds (e.g., speech) involves the respiratory system, as well as speech control centers in the cerebral cortex, respiratory centers of the brain stem, and the articulation and resonance structures of the mouth, nasal and chest cavities. However, the "organ of voice" is the larynx, a specially adapted organ located in the upper air passageway. The larynx is in the form of a triangular box, with the back and sides flattened, and a prominent vertical ridge in front; the top is broader than the bottom. Simple diagrams of the larynx are shown in FIG. 1 (FIG. 1A is a side view, and 1B is a vertical cross-section of the larynx and upper trachea). The larynx is composed of cartilages connected together by ligaments and numerous muscles; it is lined by mucous membrane that is continuous with the mucous membrane lining of the pharynx and the trachea. The vocal cords are folds located along the lateral walls of the larynx, that are stretched and positioned by several muscles. There are nine cartilages in the larynx (i.e., the thyroid, cricoid, epiglottis, and two each of arytenoid, corniculate, and cuneiform). The thyroid cartilage is the largest cartilage of the larynx, consisting of two lateral lamellae that are united at an acute angle in front, to form a vertical projection in the mid-line (i.e., the "Adam's apple").
During speech, various laryngeal muscles move the vocal cords within the lateral laryngeal walls. When the vocal cords are brought together and air is expired, air pressure from below (i.e., the lower respiratory tract) first pushes the vocal cords apart, allowing rapid flow of air between their margins. The rapid flow of air then immediately creates a partial vacuum between the vocal cords, pulling them together once again. This stops the air flow, builds up pressure behind the cords, and the cords open once more, in order to continue the vibratory pattern. For normal respiration, the muscles pull laryngeal cartilages forward and apart. Contractions of the many small slips of muscle comprising the thyroarytenoid muscles control the shape of the vocal cords (i.e., thick or thin, with sharp or blunt edges), during different types of phonation. The pitch of the emitted sound can be changed by either stretching or relaxing the vocal cords, or the shape and mass of vocal cord edges. The muscles attached to the external surfaces of the larynx can pull against the cartilages, thereby helping to stretch or relax the vocal cords. For example, the entire larynx is moved upward by the external laryngeal muscles, stretching the vocal cords for production of very high frequency sounds, and larynx is moved downward (ie., the vocal cords are loosened) for production of very bass (i.e., low frequency) sounds.
Laryngeal function may be compromised due to various causes, including upper airway obstruction, paralysis, laryngectomy, etc. Partial upper airway (i.e., the passageway from the posterior pharynx to the distal trachea) obstruction is a potentially serious condition, as the individual may lack sufficient respiratory capacity for unaided respiration or speech. Obstruction may be caused by numerous conditions, including extrinsic compression (e.g., mediastinal neoplasm, retrosternal goiter, retropharyngeal abscess, fibrosing mediastinitis, or thoracic aortic aneurysm), intraluminal obstruction (e.g., foreign body aspiration), intrinsic structural abnormalities caused by infectious diseases (e.g., epiglottitis, croup, leprosy, syphilis, and diphtheria), neoplastic disorders (e.g., oropharyngeal, laryngeal, and tracheal tumors), inflammatory and degenerative disorders (e.g., enlarged tonsils and adenoids, laryngeal or tracheal granulation tissue, cricoarytenoid arthritis, tracheobronchial amyloidosis, sarcoidosis, laryngomalacia, tracheomalacia, tracheal or laryngeal stenosis, and relapsing polychondritis), or neurologic disorders (e.g., bilateral vocal cord paralysis and functional laryngospasm).
Bilateral recurrent laryngeal nerve paralysis resulting in airway compromise is commonly encountered by otolaryngologists. Often, it is a result of thyroidectomy, although other causes (e.g., idiopathic, neurogenic, and traumatic). Traditionally, patients with bilateral recurrent laryngeal nerve paralysis were surgically treated by tracheostomy (i.e., creation of an opening into the trachea though the neck, with the tracheal mucosa being brought into continuity with the skin; the term is also used in reference to the opening, as well as in reference to a tracheotomy done for insertion of a tube to relieve upper airway obstruction or to facilitate ventilation).
Tracheostomy provides a proper airway and maintains some voice. However, this solution has been less than ideal, as most of the procedures sacrifice voice for the airway. Other treatment approaches, such as recurrent nerve decompression, exploration and neurorrhaphy (i.e., suture of a divided nerve), the nerve and muscle pedicle procedure, and various neural reanastamosis procedures have also been attempted, although they have also only achieved limited success. (See e.g., Otto et al., "Electrophysiologic pacing of vocal cord abductors in bilateral recurrent laryngeal nerve paralysis," Am. J. Surg., 150:447-451 1985!). Reanastomosis of severed recurrent laryngeal nerves usually fails or is unsatisfactory; tracheotomy is unsightly, non-physiologic, and often followed by long-term complications; arytenoidectomy is often complicated by aspiration, and always results in dome diminution of voice; and nerve-muscle pedicles are sometimes successful, although the impaired airway is not always satisfactorily restored. As stated by Otto et al., "i!t is apparent that an adequate physiologic solution is yet to be found, and the original dilemma remains unsolved, that is, improving the airway worsens voice quality and may result in aspiration. The ideal solution would be to restore an adequate airway, preserve normal phonation, and preserve the protective function of the vocal cords, thus preventing aspiration." (Otto et al., supra, at 447). These sentiments are oft-repeated in the literature dealing with rehabilitation of patients with bilateral vocal cord paralysis. (See e.g., Broniatowski et al., "Laryngeal pacemaker. Part I. Electronic pacing of reinnervated strap muscles in the dog," Otolaryngol. Head Neck Surg., 94:41-44 1986!; Broniatowski et al., "Laryngeal pacemaker. II. Electronic pacing of reinnervated posterior cricoarytenoid muscles in the canine," Laryngoscope 95:1194-1198 1985!); and Otto et al., "Coordinated electrical pacing of vocal cord abductors in recurrent laryngeal nerve paralysis," Otolaryngol. Head Neck Surg., 93:634-638 1985!).
Other situations in which voice and/or ventilation are compromised include patients who have undergone laryngectomy, due to cancer or other causes. In order to speak, these patients must use sign language, writing, esophageal speech, or use a device. Various devices have been developed in order to assist these patients, including electrolaryngeal and other devices to generate speech. (See e.g., U.S. Pat. Nos. 4,473,905, 4,672,673, 4,550,427, and 4,539,699 to Katz et al.; U.S. Pat. No. 4,547,894 to Benson et al.; U.S. Pat. No. 5,326,349 to Baraff; U.S. Pat. No. 4,821,326 to MacLeod; U.S. Pat. No. 4,706,292 to Torgeson; U.S. Pat. No. 4,691,360 to Bloomfield, III; and U.S. Pat. No. 4,571,739 to Resnick; all of which are incorporated by reference). However, many electrolarynx devices are designed to be hand-held, presenting obstacles to post-laryngectomy patient who cannot develop esophageal speech, and requires the use of both hands. In addition, such devices as the pneumatic larynx, which requires that the patient have sufficient respiratory capacity to make the device function. Development of alternative methods, such as the intraoral electrolarynx has represented an improvement. However, saliva can obstruct the intraoral larynx. Other devices include the extralaryngeal electrolarynx, which is of limited value to those patients with considerable post-radiation fibrosis of the neck. In yet another device, the transducer and intraoral tubing are attached to eyeglass frames, the activating switch is strapped to the medial aspect of the upper arm, and the power pack is carried in the pocket of a shirt or jacket. (See e.g., McRae and Pillsbury, "A modified intraoral electrolarynx," Arch. Otolaryngol., 105:360-361 1979!).
It is clear that improved means for providing speech to patients with vocal cord abnormalities, laryngeal paralysis, or laryngectomy are needed.